This invention deals generally with blenders for solid particulate matter, and more specifically with a selection control valve for blenders of the type which are vessels with a central lift column or pipe through which a gas is pumped to move material from the bottom to the top of the vessel for mixing.
Particulate blenders which are cylindrical vessels with central lift columns to raise bottom material to the top for mixing are well known in the art. They are available in versions which feed the new material into the vessel at either the bottom or the top of the vessel, and both types use a gas pumped up through the central pipe to lift material from the bottom to the top. The control valves for such blenders generally consist of several flow cutoff valves of a simple structure with each valve merely stopping or permitting flow through it.
Typically, one such valve is used to control the discharge of material out of and the entry of pressurized gas into the blender at a switching system at the bottom of the blender. A second valve is generally used to control the entry of gas into the switching system. A third valve is used to control the discharge of material from the switching system, and a fourth valve permits gas or particulate material to be fed into a bypass pipe which interconnects the bottom of the blender with the top of the blender or some other equipment. If the switching system is thought of as an enclosure with valved pipes on four sides, the pipe and valve on the top of the enclosure connect to the bottom of the blender; the pipe and valve on the bottom of the enclosure connect to the discharge pipe; the pipe and valve on one side of the enclosure connect to a source of pressurized gas, or to a source of gas mixed with particulate material; and the pipe and valve on another side of the enclosure connect to a bypass pipe going to the top of the blender or other processing equipment. With such an arrangement, it is possible for the operator to make several interconnections and select multiple operations. Clearly, with all valves closed neither blending, bypassing nor discharge are taking place. Other possibilities include: (1) with only the bottom blender valve and the gas valve open, gas is fed into the bottom of the blender, and mixing of material occurs within the blender; (2) with only the bottom blender valve and the discharge valve open, discharging of material from the blender takes place; and (3) with only the gas and bypass valves open, gas or gas and particulate material can be fed to the top of the blender. Unfortunately, however, in each of these control circumstances there is always the possibility that one or more other valves may also be opened accidentally, and that possibility can lead to the discharge of improperly mixed material. Furthermore, the use of multiple independent valves not only makes the system complex to construct and to control, but it also is quite costly and the multiple valves decrease the reliability of the system.